Hygroscopic, corrosive chemicals are frequently used in sophisticated semiconductor fabrication processes. Typical of such a chemical is anhydrous hydrogen chloride which is a colorless gas which fumes strongly in moist air. Bulk hydrogen chloride is shipped in tube trailers or Y-cylinders as a liquified compressed gas under a vapor pressure of 613 psig at 70.degree. F. Chemically, hydrogen chloride is non-corrosive in the anhydrous state. However, hydrogen chloride readily adsorbs water to yield highly corrosive hydrochloric acid, which can attack metals and other equipment, such as the containment and delivery systems, meant to provide hydrogen chloride to semiconductor fabrication facilities.
It is known to provide apparatus and methods for transfer and delivery of high purity chemicals as is set forth in U.S. Pat. No. 5,148,945, including hydrochloric acid. The patent uses vacuum to initially fill a reservoir which is subsequently pressurized with inert gas to deliver chemical to the end use application.
U.S. Pat. No. 5,137,047 discloses a process for delivery of reactive gases to a semiconductor fabrication area using a pigtail having reduced dead volume and a vacuum system which allows for purge and evacuation of the delivery system. The patent is specifically directed to the delivery of tungsten hexafluoride.
U.S. Pat. No. 4,853,148 discloses a process and composition for drying gaseous hydrogen halides, such as hydrogen chloride using a metal halide or metal halide supported on a substrate or resin.
In an article "Joule-Thomson Expansion and Corrosion in HCL System", by Paul M. Bhadha, et al. appearing in Solid State Technology, July 1992, pages S3 through S7, a discussion of the formation of liquid in conveyance of HCL through various pressure drop mechanisms is disclosed and techniques including heating are described for avoidance of such condensation, which otherwise facilitates higher rates of corrosion.
U.S. Pat. No. 4,532,778 discloses a process for recycling aqueous sulfuric acid in which the sulfuric acid is heated and separated from contained water before recycling to the reservoir of the aqueous sulfuric acid. This cycle is part of a chemical heat pump.
Presently, the industry engaged in high flow hydrogen chloride delivery for semiconductor fabrication attempts to provide high purity in hydrogen chloride using sophisticated alloys having greatly reduced corrosion rates in conjunction with traditional materials of construction. Despite the use of such alloys, such as Hastelloy, the industry has experienced corrosion of hydrogen chloride delivery systems, unstable process control and increased levels of impurity in delivered hydrogen chloride comprising either moisture or metal entrainment. The present invention overcomes these shortcomings of the prior art using a unique integration of various pieces of apparatus and processes taking into account sources of corrosion and the methods for metal entrainment in hydrogen chloride delivery, wherein the present invention enjoys the capability of delivering high purity hygroscopic, corrosive chemicals, such as hydrogen chloride, with extremely low moisture levels and extremely low levels of impurity, such as metal contaminants, below which the industry has generally been able to achieve. Such objectives are achieved by the present invention as set forth in greater detail below.